In some cases, a display apparatus switchable between a display state and a mirror state is needed. In other words, it is needed that an image-displaying surface of a display apparatus can, in some cases, turn to a mirror having reflecting function.
A typical one in these cases is an interior rearview mirror in a vehicle. A conventional interior rearview mirror is made of a mirror, by which the driver observes the environment behind the vehicle. However, it is common that passengers, luggage or the like hinder the rear windscreen so that the driver cannot observe the environment behind the vehicle via the interior rearview mirror. This results in inconvenience or even safe problems. Therefore, more and more attention is given to replacement of traditional interior rearview mirrors by display-type interior rearview mirrors.
Generally, observing the environment behind the vehicle by a display-type interior rearview mirror comes into practice by a camera installed at rear of the vehicle. The camera can be installed outside the rear windscreen, so that the field of the vision of the camera will not be blocked.
However, in some cases, a traditional interior rearview mirror is still needed. For instance, when the driver wishes to observe the situation on the back seats via the interior rearview mirror, an interior rearview camera installed outside the vehicle is insufficient to provide this function.
Therefore, for an interior rearview mirror, a display apparatus switchable freely between a mirror state (mirror mode) and a display state is needed. In particular, the mirror mode should have low power consumption. Currently, in commercially available apparatuses, which can achieve that function, a technique using translucent reflective mirror or a technique adding a polarized light-selecting unit and a polarization axis-changeable unit is typically used. These two techniques can hardly achieve bright image and bright mirror, and the power consumption at the mirror state is relatively high.
In the field of the architecture, electrochromic smart windows, which can change the color thereof according to the user's requirement and thus further adjust the sunlight irradiation level smartly, in order to decrease the energy consumption for controlling temperature indoors, have been developed. For example, the patent application CN104614913A discloses a flexible stickable electrochromic device switchable between a mirror state and a transparent state. That device is applied in portholes of an airplane, glass for daylighting, walls of a building, etc.
There is still a need for a display apparatus switchable between a display state and a mirror state.